Much like the 49ers, Antoine Bethea understands the disappointment of losing a Super Bowl.

That defeat came with the Indianapolis Colts after the 2009 season. San Francisco’s new safety also won a championship during his rookie season of 2006.

Bethea insists he is ready for another ring after finalizing his new $23 million, four-year contract with the 49ers on Wednesday, becoming a key new presence in the secondary after Donte Whitner’s departure to the Cleveland Browns.

“One of the reasons I’m here in San Fran, to try to get another ring,” Bethea said. “That’s what I’m here to do.”

Bethea announced Tuesday on Twitter he had joined the 49ers, then the team made it formal Wednesday.

The 29-year-old Bethea had 110 tackles, two interceptions and a sack last season, his sixth straight year starting every game for the Colts.

“Just as a football fan, you have to notice the talent they have on the team. You have to respect what they’ve been able to accomplish these last couple years,” Bethea said. “First of all, it’s a winning organization. From the past couple years, from outside looking in, an extremely good team. It looks like they have a ball out there on the field. Coming in, knowing this defense, a great defense, a great front seven, a great back end, I just wanted to come in and do my part.”